1. Field of the Invention
This invention relates generally to a multiple speed powershift transmission for a motor vehicle. In particular, the invention pertains to controlling temperature of the input clutches for the transmission.
2. Description of the Prior Art
A powershift transmission is a geared mechanism producing multiple gear ratios in forward drive and reverse drive and having two input clutches, which connect a power source, such as an engine or electric motor, to two transmission input shafts.
The transmission incorporates gearing arranged in a dual layshaft configuration between the transmission input and its output. One input clutch transmits torque between the input and a first layshaft associated with first, second, fifth and sixth gears; the other input clutch transmits torque between the transmission input and a second layshaft associated with third, fourth and reverse gears. The transmission produces gear ratio changes by alternately engaging a first input clutch and running in a current gear, disengaging the second input clutch, preparing a power path in the transmission for operation in the target gear, disengaging the first clutch, engaging the second clutch and preparing another power path in the transmission for operation in the next gear.
Temperature is a critical factor that determines the length of the service life of a dry powershift transmission in which each input clutch is a dry clutch. A principal failure mode is attributable to high clutch temperature, which is a durability predictor for the dual clutch of the powershift transmission.
Two clutch locations, where the temperature and degradation rate are relevant, include the clutch surface temperature, and a reference point used for temperature monitoring, which is located preferably 4.0 mm under the clutch contact surface. Although these two locations are critical to clutch durability, no direct, real time temperature feedback is available for alerting the driver of potentially abusive harmful usage because thermocouple access and the transmission of data from a thermocouple on a rotating member present technical difficulties. Additionally, when a vehicle equipped with a dual clutch powershift transmission is presented for service with clutch problems, it is difficult to trace the history of the particular problem to its root cause, and to identify possible usage conditions and anomalies.
A need exists in the industry for a mechanism to alert the operator of a vehicle with a dual clutch powershift transmission of potentially abusive conditions, combined with temperature integration for application severity and history monitoring and cumulative wear as reflected by temperature feedback.